Decomposition-controlled regime

Fig. 5.17 Temperature dependence of gas volume released during thermal decomposition of barium titanyl oxalate under heating rates (a) 50, (b) 100, (c) 300 °C/h, (d) rate controlled regime [283]...

Either of the reactions 1 and 3 given in Equations 13.1 and 13.3 can be rate controUing in the production of Rj". If the initiator and monomer are dilute, the diffusion controlled reaction 3 in Equation 13.3 may be rate limiting, whereas if monomer concentration [m] is high then the initiator decomposition reaction 1 in Equation 13.1 is rate controUing. These limits wUl be referred to, respectively, as the diffusion-controlled regime and the decomposition-controUed regime. ... 

M2-CO the first adduct bond energies are greater for Co, Ru, Pd, W, Ir, and Pt than V, Fe, Ni, Nb, and Mo. For the trimers, iron has a weaker bond than the other metals studied. For the tetramer and larger clusters the reactivity is controlled by the value of kn and no longer by the competition between uni molecular decomposition and collisional stabilization. The large cluster regime is not covered by this model used to make the correlation between kinetics and energeti cs. 

This ester resembles its methyl homologue in possessing three modes of decomposition [131]. It also supports a self-decomposition flame, the multiple reaction zones of which are clearly separated at low pressures [122, 123, 125]. Temperature and composition profiles in the low-pressure decomposition flame have been measured [133]. The products include formaldehyde, acetaldehyde and ethanol with smaller amounts of methane and nitromethane. The activation energy derived from the variation of flame speed with final flame temperature was 38 kcal. mole", close to the dissociation energy of the RO—NO2 bond. The controlling reaction is believed to be unimolecular in its low pressure regime, and the rate coefficient calculated from the heat-release profile is... 

Beginning with the work of Tenny and Waksman (1929), smdies of detrital processing have often emphasized the importance of the climate of the decomposition environment. In developing their generalized conceptual decomposition model (Figure 24), Lavelle et al. (1993) recognized that the temperature and moisture regimes usually exert the dominant control on decay. 

At the lower temperature (783 K open symbols in Fig. 70) a substantially different behavior is observed. The imide band (A in Fig. 69 bottom) decreases quasi-linearly with the elapsed time (see Eq. 24). The aromatic band (V in Fig. 70 top) is complex, revealing two distinct decomposition patterns. At the beginning (first half) of the normalized time a slow linear decrease is observed, followed by a fast decrease. The decrease of the imide band and the change of the aromatic band in the second part of the curve are typical for a film diffusion-controlled reaction of shrinking particles in a gas flow in the Stokes regime. To confirm this observation a new mathematical model is used to fit the curves [321]. Starting from Eq. 20, the reaction velocity ks is substituted with kg=D Rf1 [321]. D is the diffusion velocity and kg the mass transfer coefficient between fluid and particle. The differential equation is solved and the time necessary to reduce a particle from a starting radius R0 to Rt is obtained [see Eq. (22)] [321],... 

Most seriously lacking at the present time is information which relates to regimes of fast thermal decomposition. The degree of control now possible with... 

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